A standard belt press has a frame having horizontally extending and vertically spaced upper and lower plates defining a horizontally extending gap having an upstream end and a downstream end, vertically spaced upper and lower upstream drums rotatable about respective horizontal axes at the upstream end, vertically spaced upper and lower downstream drums rotatable about respective horizontal axes at the downstream end, and upper and lower endless belts spanned over the respective upper and lower drums and each having a working stretch lying between the plates and a return stretch. Upper and lower sets of rollers engaged between the working stretches and the respective plates can be recirculated as the belts are advanced to move with the working stretches horizontally in a transport direction to displace a workpiece in the direction through the gap so that the working stretches are supported on the respective plates by these rollers.
In standard such systems as described in U.S. Pat. Nos. 4,417,866, 4,613,293, and 5,044,269 the drums are all of generally the same diameter. Both the upstream and downstream drums, furthermore, are driven with generally the same force so that the working stretches draw the workpiece along the gap. The effect is that the downstream drums, which are responsible for pulling the workpiece through the press, do twice as much work as the upstream drums. This system works well but requires an expensive drive and relatively large-diameter drums so that neither the upstream or downstream drums are subjected to excessive stress. In fact the tensions resulting from the drive action and the bending forces are combined in the drums.